@vmacekesq: "This is certainly a standard, old question but I figure I'd ask
anyway:
I've got a little (app. 900 sf) 2-bedroom 1-story house, insulated
reasonably well - when I'm in I keep the thermostat at 82 degrees and
with a fan in the room it's comfortable. When I leave for my 9-to-5
job I bump the therm. up to 85, but at these temperatures the a/c is
still going quite a bit in my absence (the place is certainly
comfortable when I step back in, but it would be after a 20-mile
commute).
Is it more efficient to just shut the a/c off when I'm gone - does it
take a lot of energy to bring the temp back down from a standing
start, as it were?
VMacek"
    @PeterGriffin: "<quote>
Have you considered a  programmable thermostat?   Easy to install, very 
convenient (makes the temp changes for you) and tends to pay for 
themselves within months.  They even have models that  adjust 
differently on the weekend vs. weekdays.
You  can optimize energy usage by perhaps  setting the temp to 82  about 
an hour before you get home &  set it for  85-90  about the time you 
leave  for work.  With some models, you can fine tune  the temp several 
times/day, perhaps bumping it up a degree or two after you fall asleep, 
dropping it a degree or two just prior to waking up, etc.
To answer your question, it does take significant energy to recool the 
home, but it will typically be less overall vs. maintaining a 
temperature.  The savings depends how long the higher temp is maintained 
as the cost to cool will essentially offset the savings (for all 
practical purposes) while the unit is off as the temp is increasing.  
The savings is primarily due to less energy maintaining at 90F vs. 82F, 
not the warm up portion..   
The same advantages can be realized with heating, provided you are not 
using electrical (resistance) type heating as typical backup for heat 
pumps.   "
    @lshawusenet: "<quote>
It takes a lot of energy, but you save more energy.  Every bit of extra
energy it takes to bring down the temperature is equally offset by energy
saved when the temperature is rising and the A/C unit is sitting idle.
The only real disadvantage is the inconvenience of having to wait for it
to finish bringing the temperature down when you get home.  That can
take hours in some cases, and the cost savings of turning it completely
off (as opposed to just changing the set point to 85F) might not be
enough to justify it.
   - Logan"
    @rickajho: "<quote>
Shut it off. If you are gone for work at least 9 hours a day I would
have to say that it's costing you far more money to keep it running for
those extra 9 hours than any extra load on the system to get the home
back to a reasonable temperature when you return and start it. (It sure
won't take 9 hours to get the temperature and humidity levels back to a
comfortable range.) The compressor might have to run more initially when
you return, but while you are away the fan is running constantly and
eating up dollars in energy expenditure, even if the compressor is only
cycling slightly less when you aren't there.
The sure way to tell is try it both ways for a month and compare your
electric bills. But I'd bet the farm it's costing you far more to run it
an extra 9 hours a day when you aren't there.
Rick"
    @rickajho: "<quote>
P.S. Another issue that occurs to me: If you work normal 9 to 5 hours,
even with bumping the thermostat up to 85 you would still be running the
AC during the hottest part of the day - the period where it has to work
harder to keep the temperature down. Which would be the least frugal
time of the day to keep the thing running, especially if there is no one
there to get any benefit out of it.
Rick"
    @rodspeedaaa: "<quote>
And you can fix that with a programmable thermostat that starts that cooldown
so that the house will be at the lower setpoint when you arrive home.
Not likely with his house unless its rather under sized. And he
doesnt say what the temps typically get to with it turned off."
    @missingchild: "Before I had central A/C installed (do NOT use Sears for this to
learn why visit <url> I had my air
conditioners plugged into X-10 controllers.  With a telephone
controller I could call up and turn on the air conditioners just
before leaving work, so the house was cool by the time I got home.
That worked better than timers because if I weren't coming home until
late I wouldn't be wasting money cooling the house several hours
early.
Shaun Eli
<url>
Brain Champagne:  Clever Comedy For Smart Minds (sm)
<url>
The Smartest You'll Ever Laugh (sm)"
    @lshawusenet: "<quote>
Hmm, that's a neat idea.  Seems like you could do this with central
air as well, although it would be a little more complex.  You'd just
need an X-10 module, a wall wart (or other DC power supply), and a
relay.  You'd wire up the relay to switch the common line on the
thermostat, and then when turned on the X-10 module, that would
apply power to the relay (through the wall wart), which would in
turn let the current flow on the common line.  With a typical
thermostat, the effect would be the same as that of switching it
from "off" to "cool".
   - Logan"
    @dk: "<email_address> wrote in message 
news:<email_address>
<quote>
Consider this:
After you cook your supper, have you ever considered keeping the
water boiling on the stove for tomorrow's meal?
No?
Why not? It's the same principle.
Don"
    @belfert: "Rick <email_address> writes:
<quote>
I leave my AC on pretty much all the time during the summer.  I have a 
Saver's Switch that reduces my total electric bill by 15% during the 
summer.
I arrive home at pretty much the hottest part of the day.  It could take a 
long time to cool down the house at that time of day.  It takes even 
longer to cool down on really hot days as the Saver's Switch will shut off 
the A/C up to 20 minutes per hour.
I do use my programmable thermostats during the winter as it doesn't take 
long at all to heat the house."
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